Greenhouse whitefly, Trialeurodes vaporariorum (Westwood), is an important pest of greenhouse throughout the world that causes serious damage on agricultural products. In this research, some biological parameters of the pest were studied in four cucumber cultivars (Royal Sluis, Soltan, Negin and Vida) at two heights (60 and 90 cm) in a greenhouse at 19-26 °C and 80% ± 5 RH. The developmental time of all immature stages were 27.49 ± 0.34, 28.23 ± 0.3, 26.63 ± 0.24 and 27.44 ± 0.3 days, in all cultivars, respectively, but it was slightly longer at the height of 90 cm compared to 60 cm (28.65 ± 0.24 vs. 26.43 ± 0.14 days, respectively). The preimaginal mortality percent ranged from 4 to 7% in different treatments, although this difference was not significant. Female longevities were 27.9 ± 0.67, 21.35 ± 0.34, 26.71 ± 0.6 and 22 ± 0.46 days in the cultivars, respectively (P < 0.01). It was also averaged as 23.29 ± 0.4 and 26.4 ± 0.66 days at both heights. The number of eggs / female were 203.82 ± 4.89, 132.26 ± 3.57, 210.68 ± 5.31 and 162.79 ± 5.15 in different cultivars with an average of 167.66 ± 5.68 and 187.98 ± 4.75 in 90 and 60 cm (P < 0.01). The sex ratio showed no significance among the cultivars at all heights
